This invention relates to machines for forming, filling and sealing packages from a thin flat strip of flexible packaging material, the strip of packaging material being formed to a depending upwardly open tubular configuration, sealed longitudinally at overlapped vertical edge portions, sealed transversely along horizontal lines spaced vertically of the tube, and filled from above with measured quantities of product between successive transverse sealing operations. In advancing or drawing the material downwardly through a tube former at the top of the machine, it has been a conventional practice to employ end sealing bars movable in both horizontal and vertical planes. That is, the end sealing bars are intermittently moved horizontally inwardly to engage and compress the tube and are then moved vertically downwardly to feed or draw the packaging material through the former. End sealing occurs during this operation. Thereafter, the end sealing bars move horizontally outwardly to release the tube and return vertically to their starting position.
A further conventional practice in advancing or feeding the packaging material through the former involves the use of a vacuum belt mechanism. A pair of perforate endless belts are disposed respectively on opposite sides of the tube to engage and feed the same downwardly through a reduced pressure or vacuum condition at the openings in the belt. End sealing bars in this arrangement may be stationary vertically but movable horizontally to intermittently engage and transversely seal the tube between feed and product drop or fill operations.
In both of the foregoing arrangements, a relatively long "product drop" is encountered. That is, the distance the product must fall from the discharge end of the hopper within the former is substantial. With the vertically movable end sealer arrangement the necessary vertical travel of the end sealers results in a substantial vertical distance through which the product must fall in the filling operation. Additionally, it should be noted that the portion of the tube immediately above the end sealer is in tension and is drawn into a relatively sharp or tight "V" configuration during the downward movement of the end sealers. This configuration is not conducive to a good filling operation nor is the resulting stress at the end seal conducive to good end sealing.
In the vacuum belt arrangement, belt and end sealer movement can be coordinated to provide for a relaxed condition of the tube above the end sealer, a relatively shallow or loose "V" configuration with a slight bulge or ballooning effect, and this is conducive to a good filling operation. End sealing may also efficiently accomplished in the absence of stress during sealing. The inner or operative runs of the vacuum belts, however, extend through a substantial vertical distance and a relatively long product drop distance is again encountered.
A long product drop is generally acceptable for relatively heavy material allowed to fall freely from the hopper into the tube in measured quantities. This is not the case, however, with relatively light product material such as potato chips. A condition known as product "string-out" is encountered with light materials wherein air resistance causes the upper portion of the mass of descending product to decelerate relative to the lower portion thereof. That is, a number of potato chips at the top of a mass of chips may tend to "string-out" vertically above the major portion of the mass as the product falls into the tube. Obviously, the time required for each filling operation is significantly increased by "string-out". This results in a severe limitation on the overall speed of operation of the machine and production rates are detrimentally affected.